A storage server is a special-purpose processing system used to store and retrieve data on behalf of one or more client processing systems (“clients”). A file server is an example of a storage server. A file server operates on behalf of one or more clients to store and manage shared files in a set of mass storage devices, such as magnetic or optical storage based disks or tapes. The mass storage devices may be organized into one or more groups of Redundant Array of Inexpensive Disks (RAID). In a storage area network (SAN), a storage server can provide clients with block-level access to stored data, rather than file-level access. Some storage servers are capable of providing clients with both file-level access and block-level access, such as certain Filers produced by Network Appliance, Inc. of Sunnyvale, Calif.
Among the uses of a storage server, including a file server, is the essential process of saving backup copies or archives of files to enable retrieval of files after such files have been modified, deleted, or otherwise lost. In certain operations, it is common to make a regular series of backups of data files, and to possibly make interim backups of changed files in between full backups. The more often that data is backed up, the more likely it is that lost files in a particular desired form can be recovered.
However, backup copies inevitably require storage space, and frequent backups can create significant storage space requirements. Even if archives are eliminated after they reach a certain threshold age, it is common for a system to include images of older data that is no longer required. The storage of this unneeded data wastes space that is contained in or that is managed by the storage server, and the amount of unavailable space can increase as more frequent backups are performed.